级联多电平逆变器全调制比的特定谐波消除

级联多电平逆变器采用阶梯波调制策略虽然能够产生所需要的基波电压而又不产生低次谐波,但该方法只能在很高的调制比下才能应用,而在中低调制比下不存在具有实际意义的解.为了解决这个调制宽度问题,提出了用多段调制模式的办法来计算级联多电平逆变器的开关角度.本文中利用四段式的方法证明了在中低调制比下,具有实际意义的开关角度仍然存在.针对特定消谐方程组的求解,本文提出一种高效的同伦迭代计算方法,通过将非线性方程组转化为偏微分方程组,然后采用龙格库塔法对其进行求解,最后将该值作为迭代算法的初值继续计算即可求得.对比其他的迭代法,该方法具有很宽的收敛范围.实验结果证明了这种多段式调制模式以及同伦迭代算法的可行性和正确性.

Selective Harmonic Elimination for All Modulation Indices of Multilevel Cascaded Converter

This paper presents a multi-pattern method which is employed to compute the switching angles in a multilevel converter so as to produce the required fundamental voltage while at the same time not generate the selective harmonics. Using a staircase fundamental switching scheme, previous work has shown that it is possible to produce solutions only for higher ranges of the modulation index. Here four patterns are shown to extend the lower range of modulation indices for which such switching angles still exist. A unified approach called homotopy algorithm is presented to solve the SHE equations for all of the various switching patterns. The nonlinear and transcendental equations with homotopy algorithm from mathematical point is analyzed mainly in this paper. In particular, it is shown that all patterns require solving the same set of equations where each pattern is distinguished by the location of the roots of SHE equations. In contrast to iterative numerical techniques, the approach here can produce all solutions in a large convergence extent. The experimental results verify the precision of the multi-pattern method.